U.S. Pat. No. 3,940,229 describes a mold for making concrete masonry units with a roughened texture on at least one face. The mold has a wall with an inwardly extending lip on the lower edge of the wall. The lip is rectangular in profile, and may be solid or serrated to provide sawtooth-like projections. As the formed concrete unit is forced out of the bottom of the mold, the patent says that the lip produces a scraping or tearing action on the adjacent face of the concrete unit, so as to produce a roughened surface on it. We have experimented with this type of mold, and found that it does produce a roughened surface on the concrete unit, but that the face sometimes has a slight "shingled" appearance.
Angelo Lane Incorporated of Carnegie, Pennsylvania has also, for many years utilized a similar mold to produce a roughened textured face on concrete masonry units. Lane's mold includes a bead of weld material along the lower edge of a mold wall. Generally parallel grooves about one quarter inch wide are ground into the bead at about half-inch intervals. The grooves have been oriented both parallel to the direction of travel of material through the mold, and at an angle thereto.
U.S. Pat. Nos. 5,078,940 and 5,217,630 also describe a mold for making concrete masonry units with a roughened texture on at least one face. The mold described in these patents also employ an inwardly extending lip on the lower edge of at least one wall of the mold. In this case, the lip is wedge-shaped in profile. In addition, the mold includes a plurality of projections above the lip on the same wall and a mesh extending upwardly from the lip generally parallel to the wall and spaced inwardly from the wall. The projections and the mesh are adapted to hold a portion of the concrete fill material against the wall as the formed concrete unit is forced out of the bottom of the mold. As described in these patents, the concrete material held against the mold wall by the projections and the mesh is sheared from the concrete material forced out of the mold, thus forming a roughened surface on the concrete unit forced from the mold. We believe that molds of this design, although without the mesh, have been commercialized under trademark Softsplit. We do not have any direct experience with the Softsplit molds, but understand from those who have used them, that the process must be occasionally interrupted to clean out the material that agglomerates around the projections. This is not necessarily an easy cleaning process. It depends upon how accessible the mold face is to the machine operator. In many of the commonly used concrete block machines, the mold faces are relatively difficult to get at, and safety dictates that precautions such as machine lockouts and the like be used when the cleaning process is undertaken. Unlike this Sofsplit style mold, the mold of the '229 style is self-cleaning. The small amount of material that remains loosely adhered to the lipped mold wall after the mold is stripped is knocked clear of the wall when the next machine pallet is placed against the mold bottom.
U.S. Pat. No. 5,879,603 describes an improvement to the '229 style mold. The '603 patent describes a mold with a wedge-shaped lower lip and an opposed upper lip spaced apart from the lower lip by the distance defining the height of the concrete unit to be produced. The mold acts in a similar fashion to the '229 style mold, but produces less "shingling" effect on the roughened face, and is also self-cleaning in the same fashion: the concrete material that loosely adheres to the mold wall above the lower lip is knocked off the wall when the next pallet is brought into place beneath the mold.